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# Introduction to matlab

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### Introduction to matlab

1. 1. INTRODUCTION TO MATLABTM http://www.matlab.com General instructions Open the Matlab program and input commands into the text-based window. Type help <function name> to obtain information on Matlab functions. Example help sin will provide information on the sin function. lookfor <keyword> to do a key word search. Ctrl + C to abort command. pwd shows the current working director. dir shows a file listing. cd changes directory to the one specified e.g. cd a: will change to the a drive. who displays the variables in the workspace. clear clears the working directory. Calculations using Matlab Calculations may be done in the Matlab Environment using the following operators +, -, *, / which represent addition, subtraction, multiplication and division. Other useful mathematical functions are sqrt, ^, sin, asin, cos, acos, tan, atan, log(base e) log10(base 10), abs, angle. Programming environment Variable names may be used for example if we let a=1, b=3, c=4, we can then set d=a+b+c. d will equal 8. Variable names are case sensitive, can have up to 31 characters, they must start with a letter and cannot contain punctuation. Plotting functions Results may be plotted using the plot, subplot, axis and hold functions. Plot details can be included using the title, xlabel and ylabel functions Two vectors (list of numbers) e.g. V for voltage and I for current with 20 elements each can be plotted using the following syntax. plot(I,V), title('Ohms Law'), xlabel('Current / Amps'), ylabel('Voltage / Volts’). A vector (list of numbers) with a variable name V is written into Matlab as V = [ 1 2 3 4 5 6 7 8 9 10 ] note space between numbers. Script m-files A sequence of Matlab commands can be put together and run in sequence by saving a text file with the commands as an m-file. There is a convenient text editor in Matlab. Go to file - new m-file to start text editor or file - open m-file. A very useful command that can be used with m-files is the input function. Example of how to request information for variable x x = input(‘Enter value for x (state units) ’) Comments can be added to the m-file if a % sign is placed before the comment.
2. 2. INTRODUCTION TO MATLABTM http://www.matlab.com Vectors and Matrices Vectors (list of numbers) and matrices are conveniently formed in rows. Square brackets enclose the vector or matrix, commas separate elements of a row and semicolons separate rows ( the commas can be excluded if a space is left between row elements). Vector A=[ 2, 3, 4 ] or A=[ 2 3 4 ] Matrix B=[ 3, 5, 6 ; 2, 6, 3 ] or B=[ 3 5 6 ; 2 6 3 ] To transpose a vector or matrix use the ' operator. Functions for producing vectors and matrices are: rand, round, max, min, colon, linespace, logspace, zeros and ones. Matrix operations Operaion Matlab Element by Element Addition A + B A + B A + B Subtraction A - B A - B A - B Multiplication A x B A * B A .* B Division A / B A / B A ./ B Indexing elements of vectors and matrices: The first element of a vector is indexed by, 1 and the top left corner of a matrix is indexed by (1,1) Indexing examples a=A(2) will make variable a =3, b = B(2,2) will make variable b = 6. Flow Control Matlab has a number of flow control functions similar to standard programming languages such as C programming e.g. for, while, and if else. Function files Function files are similar, to m-files except they have a formal set of input and output variables. They are similar to sub routines in other programming languages. The first line of the script must have the following format: function [outputVariableList] = functionName(inputVariableList) the m file name must be the same as the functionName